1. Field of Invention
The present invention relates to a coil inductor. More particularly, the present invention relates to a method of manufacturing a coil inductor to reduce energy loss in the substrate.
2. Description of Related Art
Traditional inductors fabricated on silicon substrate are provided by coils of conductive material formed on the substrate. The coil of conductive material may be formed in a spiral structure as a spiral inductor in dielectric film. As illustrated in FIG. 1, a top view of a spiral inductor, the traditional spiral inductor is a spiral structure with the inductor coil 102 flatly laid out on the substrate surface 104. The two ends 106, 108 of the coil 102 may be electrically connected to conductive pads, respectively. The current flows through the inductor coil 102 introducing an inductance L and a quality factor Q. The current through the inductor coil also induces a small current known as the Eddy current flowing in the substrate.
Eddy current can be viewed as wasted power dissipation in the substrate. This creates an energy loss to the inductor, which then lowers the Q of the inductor degrading its performance. The Q factor is defined as the ratio of the energy stored in the inductor and the power loss by the inductor. Therefore, when more power loss is generated by the Eddy current, the more it reduces the Q. Thus, a design challenge for inductors manufactured on silicon substrates has often been of how to reduce the generation of Eddy current.
For the forgoing reasons, there is a need for an inductor structure having a large quality factor inducing less Eddy current in the silicon substrate.